U.S. Pat. No. 6,114,632, issued on Sep. 5, 2000 to Planas, Sr. et al. (“the '632 patent”) disclosed a hybrid electrical cable. A hybrid electrical cable is an integrated, insulated electrical cable that combines both power conductors and voice/data signal conductors overlaid by an outer insulating sheath or jacket. The '632 patent hybrid cable included a first group of one or more conductors for transmitting AC power and a second group of one or more conductors for transmitting voice or data signals. Because of the proximity of the power conductors and the voice/data conductors, shielding and/or isolating the data/voice conductors from electromagnetic emissions emitted by the power conductors was of paramount concern. A first insulation sheath enclosed the first group of one or more power conductors. A second insulation sheath enclosed the second group of voice/data signal conductors.
The '632 patent disclosed that the first and second insulation sheaths included an inner layer of organic compound material and outer layer of magnetic material. The magnetic material preferably was barium ferrite. The barium ferrite layer in the first and second insulation sheaths advantageously isolated the second group of voice/data conductors from the magnetic field generated by the first group of power conductors.
The advantages of providing a single integrated cable having both power and voice/data conductors has obvious cost and installation advantages compared with utilizing two or more separate power, data and/or voice lines or cables. The '632 patent is incorporated in its entirety herein by reference.
While the hybrid cable disclosed in the '632 patent represented a significant advance over state of the art electrical cables, additional improvements were desirable, including making a cable having improved electromagnetic absorption and shielding capabilities, greater power and data capacity and being easier and less costly to manufacture. What is desired is a hybrid cable with improved electromagnetic absorption and shielding capabilities, greater power and data capacity and which is efficient to manufacture.
Additionally, in spite of the obvious advantages of a hybrid cable capable of high voltage power transmission and low power signal transmission on a unitary structure cable, there are certain situations in which is it desirable to install a high voltage power cable adjacent low voltage signal conductors in metal or plastic conduit or raceway. For example, in an existing commercial or industrial building that utilizes metal or plastic conduit or raceway to route power conductors, it would be very advantageous to use the existing conduit or raceway systems to route both high voltage power (via a power cable) and low power signal conductors (via one or more signal conductors or cables) thereby providing both power and voice/data transmission via the existing conduit/raceway system.
One problem encountered with running power and data/voice signal conductors in the same conduit is the fill ratio for metal and plastic conduit set forth in the National Electrical Code (N.E.C.). The fill ratio limit means that the total cross sectional area of all conductors (including insulation jackets and sheaths) routed through a section of conduit must be less than specified amount of the internal cross sectional area of the conduit.
An even more serious problem encountered with an adjacent arrangement of power conductors and data/voice signal conductors within a section of conduit is that of loss or disruption of signal transmission that would result from external high frequency transients imposed on one or more of the power conductors of the power cable, e.g., a high frequency transient caused by lightening hitting a power line coupled to the power cable. Because of the proximity of the power cable and the signal conductors disposed in the conduit or raceway, such a high frequency transient traveling along the power cable is likely to interfere with low power signals in proximity to the transient thereby causing a serious loss of signal integrity on the low power signal conductors. Indeed most electrical codes forbid the use of power conductors adjacent data conductors in a section of conduit unless there is proper shielding of the power conductors to protect the signal conductors from such transients.
What is also needed is a high voltage power conductor cable that can be utilized adjacent one or more low power signal conductors in a length of metal or plastic conduit or raceway. More specifically, what is desired is a power conductor cable that has a minimum cross sectional area for conduit fill ratio purposes and that has sufficient electromagnetic field shielding to reduce the probability that high frequency transients imposed on the power cable will cause significant loss of data/voice/control signals being transmitted on low power signal conductors adjacent the power cable.